I'm on High Sierra. If I click the green button (Firefox window) the window goes to full screen. Then, if I raise the cursor to the very top edge of the screen, the menu bar reappears and I can click the green button again, which returns the window to its original size.
iMac (19,1, 3.1 GHz i5, 12.7.4, 40 Gb RAM); MacBook Air (1.8 Ghz, 8 Gb RAM, 10.14.6, 256 Gb SSD) Vodafone router and Devolo Wi-Fi Extender, Canon TS8351 printer/scanner.
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